Metadata literally means data about data. In other words, metadata are information associated with a piece of data that describes or characterizes the associated piece of data. For example, in a database, one data item may be a phone number, another a name and another an address. The address may have metadata associated with it that indicates: “this is an address” or “this address came from the current phone book,” or “this address was entered by John”. Consequently, metadata can be used to sort or organize the database in many different ways. Metadata can also simply provide additional information about the source or other aspects of the data that may be important to a user. For example, metadata may specify the type of data, one or more relevant categories the data belongs to, the source of the data, who input the data, when the data was input, etc.
If the metadata are, for any reason, removed, the data itself is not changed in any way and can still be used to the extent the application using the data does not rely on associated metadata. Extending the example above, if an address is associated with metadata indicating that the address was taken from the current phone book, a user can readily obtain a list of all addresses in the database that came from the current phone book. If the metadata are removed, the user can still use the address data as an address, but will probably not be able to readily determine the source of the address data.
Metadata are commonly used in a wide variety of applications. For example, meta-tags are a specific form of metadata. Meta-tags are associated with web pages on the Internet and usually include key words that describe the content of the associated web page. Meta-tags are then used by search engines to classify web-pages and identify pages of potential interest in response to a user's search. Metadata are also commonly used in organizing electronic files on a computer system. Metadata associated with each file may identify when and by whom the file was created, the size or type of the file, and other information.
In particular, metadata can be used with electronic image files. For both business and personal applications, people now create large amounts of digital images every day. Frequently those images are shared by transmission over the Internet. Because of this increasing use of digital images, problems arise in the effective use, categorization, cataloging and sharing of these images. Consequently, metadata are often generated and included in the image file. Currently, almost all digital cameras generate a standardized set of metadata according to a standard known as Exchange Image File Format (EXIF). The EXIF standard was created by the Japan Electronic Industrial Development Associate (JEIDA), a Japanese consortium of companies that make digital imaging products. An EXIF standard was released in October 1995 and revised in November 1997. Under the EXIF standard, as the image file is created, for example as a “.jpg” or “.tif” file, an EXIF header is appended to the file containing metadata about the image. This metadata may include such items as when the image was created, the equipment and settings used, etc.
Additionally, the Digital Imaging Group (DIG) has created new specifications, known as the DIG35 Metadata Specification, that transform images into self-contained information modules. The Digital Imaging Group (DIG) is a consortium of many industry leaders in graphics, imaging and software. DIG35 member companies collaborated to create a specific set of metadata for describing elements of an image. The DIG35 Metadata Specification provides a comprehensive set of metadata definitions that will supply standard classification of objects.
Using metadata, information can be added to digital image files to supplement the pixel or image data itself. Information can be added about subject matter, how and where the image was created, by whom, what usage is appropriate, categorization and more. Photographers are able to log information about camera settings, copyright information or image manipulation techniques within the image itself.
The practical uses of metadata in electronic image files are abundant. For example, a user can search for an image based on subject matter using keywords encoded in the image file as metadata. For image sharing, metadata can be used to caption or tell the story behind the images.
Given the importance or potential importance of metadata in image files, it becomes important to safeguard and maintain that metadata within the corresponding image file.